1. Field of the Invention
The present invention relates to waste tank servicing assemblies and more particularly to a combination of a flowmeter with a flow valve assembly operating a fluid operated waste drain valve and spray/rinse apparatus adapted to be installed in an aircraft lavatory waste tank.
2. Description of the Prior Art
In some aircraft lavatory systems currently in use, a common waste tank is provided in conjunction with more than one lavatory unit. In others, a tank is provided for each lavatory. During a flight, the waste tank, which may be used with a recirculating toilet system or, alternatively, with a fresh water system, is utilized to retain human wastes. At the conclusion of a flight, the tank is drained and cleaned by ground service personnel. During that process, the tank is rinsed out with a cleaning fluid which may include deodorants and disinfectants, and is provided with a predetermined quantity of precharge liquid (depending on the installation), prior to the next flight of the aircraft.
In waste systems of the prior art, the tank drain valve is connected through a cable assembly to a manual release mechanism which is located at the service panel. As noted in U.S. Pat. No. 4,338,689, issued July 13, 1982, to Clifford V. Zieg and assigned to the assignee of the present invention, alignment problems were encountered with a valve that was manually operable through a cable. Prior art systems employed a long rigid extension tube to assure continued alignment of the valve in the valve seat. The patent to Zieg, however, illustrated a novel, elastomeric valve plug which could accommodate some degree of misalignment and still form an adequate seal for the tank.
The tanks of the prior art also included a special drain fitting or nipple which was adapted to connect to a servicing vehicle. The vehicle supplied a cleaning and rinsing fluid to an intake port which applied the fluid to the interior of the tank through a spray system. After the drain valve was seated, the same spray system was used to impart a premeasured precharge to the tank, necessary for recirculating toilet systems.
In servicing a waste tank according to prior art, a technician would couple a waste line to the nipple at the service panel. The technician would then manually, through use of a cable into the coupled waste line. A cleaning fluid line would then be connected to the intake port and a combination of a cleaning and disinfecting fluid was applied through a spray line, cleaning the interior of the tank while the drain valve was kept open.
After a predetermined time interval, usually after the prescribed volume of fluid had been delivered, the drain valve would be closed by releasing the cable. The tank was then filled to approximately 75% capacity by permitting additional, rinsing/cleaning fluid to be supplied until the predetermined quantity of fluid had been furnished. The technician would then manually dump the tank contents again and finally fill the tank with a precharged quantity. Tank trucks frequently are fitted with meters which display the quantity of fluid that has been delivered.
The prior art system became a source of at least two major problems, even with the modified drain plug of the Zieg invention. One problem was cable breakage which required a partial disassembly of the tank and aircraft to reinstall a new cable system. In addition, the various elements of the cable system required service and maintenance and, because of the hostile environment, from time to time would become inoperable, preventing the operation of the drain valve.
A second, potentially more serious problem is the service technician, who, either through inattention or carelessness, fails to shut off the cleaning/rising supply after the specified volume has been furnished or time interval has elapsed, resulting in an excessive precharge in the tank. In some instances, this could impose a premature limit on the usage of the lavatory, since, once the tank is determined to be full, further usage is prohibited. Since this circumstance usually occurs during the flight, those lavatories which are coupled to the tank must be taken out of service.
A more serious consequence of technician inattention is the overflow of the tank during servicing. Serious structural damage to the aircraft could result since the cleaning/rinsing fluid tends to be highly corrosive to metallic parts. Moreover, any overflow into the lavatory compartment or into the inaccessible interior of the fuselage of the aircraft creates a potential hazard to the integrity of the structural and control elements of the aircraft.
U.S. Pat. No. 4,584,726, issued Apr. 29, 1986, to Grills, et al., and assigned to the assignee of the present invention illustrated a waste drain valve assembly that automatically opens upon the application of cleaning/rinsing fluid and at the same time provides a predetermined quantity of precharge fluid to the tank, specific to the type of aircraft being serviced without any special attention required of the service technician. The service technician merely attaches a line providing cleaning and rinsing fluid to an intake line leading to the waste drain valve assembly and shuts down the system after a prescribed time interval has elapsed. A built-in precharge reservoir then supplies the proper quantity of fluid as a precharge, after the valve has closed.
Although the improvements of the Grills, et al., invention eliminates the possibility that the service technician will give the tank an excess precharge, his attention is still required to insure that the fluid is delivered to the waste drain valve assembly for the proper fluid quantity or minimum time interval necessary to drain and rinse the tank. Carelessness or inattentiveness of the service technician could result in wasteful quantities of cleaning/rinsing fluid being run through the system, since any quantities of fluid in excess of the amount required to rinse would be emptied through the fluid operated drain valve.
What is needed, and what has been provided in the present invention, is a system that measures the delivery of fluid to the waste drain valve and automatically terminates the cleaning cycle upon delivery of a predetermined quantity of fluid. The service technician need only hook up the fluid supply line to the fluid intake line, turn on the fluid supply and the system insures that the proper measure of fluid is delivered to the waste tank, freeing the service technician to do other tasks.
3. Summary Of The Invention
In a preferred embodiment, an improved lavatory waste tank cleaning system includes a flow meter which activates valves that provide fluid to a fluid operated waste drain valve and to a rinsing and cleaning system. The flow meter is coupled to the intake port and meters the delivery of fluid to the system.
In the preferred embodiment, the flow meter operates the flow valves through an electronic counter and solenoid valve system. The flow meter delivers a train of electronic pulses to the electronic counter. The electronic counter recognizes a predetermined pulse count and opens and closes a pair of solenoid valves, in a predetermined sequence, alternatively delivering fluid to the waste dump valve and the cleaning/rinsing system, and to the waste tank. A rechargeable battery power supply energizes the electronic system in the absence of other sources of power. The battery is charged during flight. A pressure switch may be included which suppresses the counter until a predetermined pressure is reached in the line. The pressure switch can also function to hold the valves closed at the completion of a cycle until the pressure drops below the predetermined level.
In the preferred embodiment, the initial provision of fluid flow through the first flow valve into the fluid operated waste drain valve operates the drain valve, dumping the contents of the tank. As the valve is held open, additional fluid is routed to a rinse-spray structure which cleans the interior of the tank. After a predetermined volume of fluid flows through the flow meter, the counter signals the closing of the first, normally open solenoid flow valve.
One typical waste drain valve is disclosed in the recently issued U.S. Pat. No. 4,584,726, to Grills et al., assigned to the assignee of the present invention. The drain valve includes a hydraulic piston with a return spring whose force can be overcome by fluid pressure. The flow from the pressurized source of fluid, usually a service vehicle, thereby opens the drain valve. The continued provision of cleaning/rinsing fluid to the system through the normally open first flow valve maintains the drain valve in the open position.
Fluid flowing through the first flow valve and piston chamber enters the spray rinse system through a check valve. The continued provision of fluid under pressure to the first flow valve thus provides for the simultaneous cleaning, rinsing and draining of the waste tank.
When enough fluid has been supplied to the system for rinsing the waste tank, the counter commands the energizing of the first solenoid flow valve, closing it to further flow. The fluid pressure at the waste dump valve is reduced, enabling the force of the return spring to overcome the force of the fluid pressure, thereby allowing the waste drain or dump valve to close.
A second, preprogrammed volume of fluid is now provided to the second flow valve which delivers it directly into the waste tank through the spray rinse system. The second flow valve remains open for a premeasured quantity of fluid. The counter signals the second solenoid flow valve to close after the proper quantity of fluid has been dispensed to the tank. An optional signal lamp can be placed at the service panel to indicate to the service operator that the cycle has been completed.
When the operator at the source of fluid recognizes that the cycle is completed, he may cut off the fluid supply to the intake line and the flow meter. Where a pressure switch is used, the valves are held closed until the fluid supply is cut off. The first flow valve then opens in readiness for the next cycle. The fluid already in the waste tank then serves as a "precharge", which can prevent wastes from adhering to "dry" areas of the tank and, more importantly, provides the necessary "precharge" or minimum volume needed for operating a recirculating toilet system.
Because aircraft in a servicing area frequently lack an on board power supply, in the preferred embodiment, the system has a built in power supply which operates with a small rechargeable battery. The battery is charged by the aircraft electrical power system during flight. In the absence of other sources of power, the battery is sufficient to provide power to the flowmeter, the electronic module and the solenoid valves during the cleaning cycle.
In an alternative embodiment, a positive displacement flowmeter is driven mechanically and operates the flow valves by rotating a programmed control valve that delivers a predetermined volume of fluid to the waste drain valve and the cleaning system. The control valve has fluid flow orifices in its walls which are positioned to alternatively provide fluid to the waste drain valve and the cleaning system, depending on the rotational position of the control valve. The flowmeter thus rotates the control valve through various stages of its cycle, depending on the volume of fluid delivered to the flowmeter.
In other embodiments, the measurement of fluid is accomplished by liquid level sensors that are positioned in the waste tank. A first sensor indicates that the tank is empty, a second sensor could signal the appropriate precharge level and a third sensor would signal that the tank is at its fill limit. An additional sensor could signal an intermediate fluid volume which could be used during the cleaning cycle to command opening of the waste drain valve during the "rinse" portion of the cycle.
It is within the scope of the present invention to use alternative configurations of apparatus and to measure the fluid usage differently. For example, one alternative method of operation would utilize a timer and impose a different sequence of actions. Since most tanks are provided with one or more liquid level sensors, it is possible to apply fluid to the first solenoid valve opening the hydraulically operated drain valve. After a brief interval sufficient to drain the contents of the tank, the first valve can be energized to close, thereby closing the drain valve, as well.
The second solenoid valve can then be energized, providing fluid to the waste tank until an intermediate liquid level sensor signals a partially full tank. The second valve can then be closed and the first valve reopened, operating the drain valve and again dumping the contents of the tank. The first valve is again closed and the second valve opened, this time to deliver the precharge. One of the liquid level sensors is positioned to signal when an adequate amount of precharge has been added to the tank, at which time the second valve is again closed and the cycle is completed.